fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-MERGE-1042987

Author: snyk-bot

package.json

@@ -24,7 +24,7 @@
     "moment-timezone": "0.4.1",
     "object-assign": "4.0.1",
     "react": "15.4.0",
-    "react-native": "0.38.0",
+    "react-native": "0.49.0",
     "react-native-keychain": "0.2.6",
     "react-native-mock": "0.2.7",
     "react-timer-mixin": "0.13.3",